I’ve spent enough time around scientists and engineers to be fascinated by certain personality and cognitive traits that are far more ubiquitous among them than in the general population. Analytic mindsets, obsessions with problem-solving, taxonomizing, and other traits fuel the work ethic of engineers.

How they apply it to more abstract and unsolvable questions, however, can vary quite a bit. And that shows in the book. Just contrast Caslav Brukner’s post-Cold War individualism–

BRUKNER: Totalitarianism was the biggest tragedy of the twentieth century. With lasting danger of an increase in the influence of collectivist ideologies, it is important for us to continue to study them so we can learn how to avoid them, or oﬀer resistance to them when they are on the rise, or diminish their consequences when they get to power. Thus far, I’ve had the opportunity to be exposed to three ideologically diﬀerent social structures: Tito’s socialism, with “workers’ self-management” as a propaganda façade for continuing a one-party political monopoly; Milosevic’s brutal and manipulative nationalism; and finally, Austria’s liberal democracy, with its everyday latent-but-pretty-obvious xenophobic political reality. In reaction to these experiences, I have developed a firm conviction about the importance of independence and self-reliance, and about the importance of opposing external interference with one’s own beliefs and desires and with the beliefs and desires of those we love and care about.

–with American Chris Fuchs’ golly-gee-whiz subjectivism–

FUCHS: One of my favorite movies of all time is Frank Capra’s It’s a Wonderful Life. If you ask me, the message of quantum theory’s necessary violations of the Bell inequalities is the same as the message of this movie—that our actions matter indelibly for the rest of the universe (pluriverse).

Quantum theory on the other hand, we Quantum Bayesians believe, carries the principle of independent existence to a much more satisfactory level. Wigner and his friend really do have separate worlds, modulo their acts of communication—and so of all physical systems one to another. It signals the world’s plasticity; it signals a “wonderful life.” With every quantum measurement set by an experimenter’s free will, the world is shaped just a little as it participates in a kind of moment of birth.

Quantum Bayesianism, as far as I can tell, is a blatantly idealistic metaphysics that, instead of removing the observer from the quantum picture, as de Broglie, Bohm, Everett, and many others have tried to do, shunts more of the world into the observer. I have to admire the audacity. Fuchs’ work has been influential in quantum computation as well, so the metaphysics aren’t a gating factor on its usefulness. But Fuchs’ tone grates on me, because it seems to minimize the sad truth that many people’s worlds are filled with frustration, sadness, and suffering–much of it not by their own doing. Even if Fuchs’ views turn out to be 100 percent right, I will remain more sympathetic to Brukner’s attitudes.

Brukner does, however, approve of the move to an information-theoretical approach, disagreeing with the more hard-headed contributors that acts of measurement can simply be factored out of quantum mechanics.

The most sarcastic phrasing of the hard-headed view was John Stewart Bell:

BELL: What exactly qualifies some physical systems to play the role of ‘measurer’? Was the wave function of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system … with a Ph.D.?

Unfortunately, I cannot judge how convincing Brukner’s rejoinder is:

BRUKNER: Once we accept that probabilities are irreducible, the role of the observer is explicitly introduced into the theory. This is for the simple reason that she, by choosing the measuring device, can decide on the basis of her free will which measurement context will be realized in the actual run of the experiment. But due to the randomness of the individual quantum outcome, she cannot influence which particular outcome will occur in the chosen context. Zeilinger put the point this way: “The observer has a qualitative but not a quantitative influence on reality.” Therefore, the observer in quantum mechanics has a participatory role in forming reality.

By contrast, in a theory describing observation-independent reality, like in classical physics, the observer has only a passive role, as her actions can always be interpreted as revealing the values of physical quantities that all coexist and are independent of which experiment is actually performed. The reader may object that my explanations are anthropocentric and that I overestimate the role of the observer. Let me be clear: I am not saying that quantum theory makes sense, or is valid, only if observers are there. The “measurement context” can be induced by the prevalent basis of the environment surrounding the quantum system, without invoking any observers. Yet the mere possibility that an observer can choose the measurement context, isolating the quantum system from environmental interactions that select a preferred basis, is exactly what gives her a fundamental role in the act of observation. This is a major intellectual step forward over naive classical realism.

So even though Brukner and Fuchs are broadly in sympathy, Brukner does not generalize from the theory to Frank Capra.

The sensible-sounding Jeffrey Bub says something similar:

BUB: This is, in broad outline, what I would call an information-theoretic interpretation of the nonclassical features of quantum probabilities, in the sense of Shannon’s notion of information, which abstracts from semantic features of information and concerns probabilistic correlations between the physical outputs of an information source and a receiver. On this view, what is fundamental in the transition from classical to quantum physics is the recognition that information in the physical sense has new structural features, just as the transition from classical to relativistic physics rests on the recognition that space-time is structurally diﬀerent than we thought. This seems to me the interpretive program that makes the best sense of quantum mechanics.

And indeed, the more optimistic of the book’s contributors seem to see an information-theoretical perspective as one that helps make some metaphysical sense of quantum mechanics.

The more hard-headed sorts, whether physicists like GianCarlo Ghirardi, mathematicians like Shelly Goldstein or philosophers like Tim Maudlin and Guido Bacciagaluppi, want to get rid of the seemingly fuzzy concept of an observer/measurer/agent and be left with something closer to physics as it has been known, where the math is clearly a modeling tool used to explain things in the world. Even the Everett many-worlder David Wallace falls into this category. (At one point, I believe Wallace calls the Everett many-worlds interpretation the most conservative interpretation of quantum mechanics, which should give some idea of how big these problems are.)

Lee Smolin splits the difference by accepting the information-theoretical approach but then citing it as evidence that quantum mechanics isn’t fundamental anyway.

The peculiar thing is that the idealists seem to be at odds with the Platonists. That is, the ones who want a full-fledged, independent world of mathematico-physical Forms are the ones who do not want the observer to play any part in the construction of that world of Forms. The laws are there, we observe and see what happens, and from empirical reality and deep thinking we come up with a picture of the World of Forms. But material reality is still the interface, and our acts are fundamentally acts of observation. So Ghirardi, Goldstein, and Maudlin seem to adopt what is more or less a materialist-Platonist view in practice, if not in theory.

Whereas the subjectivists like Fuchs and Lucien Hardy and David Mermin believe that our minds play a part in forming the world prior to the set establishment of that apparent world-to-experience. Fuchs doesn’t present his philosophical views in enough detail for me to figure out exactly what constitutes “world-shaping” or “plasticity” (or else I don’t have enough of the context to infer it), but it seems fairly clear that he wants a world of constant becoming in which we actively play a part.

And yet this ironically restricts our ability to know the entire cosmos, because in Fuchs’ view the entire cosmos doesn’t “exist” in the conventional sense–it’s a “pluriverse.” It’s not just subjective idealism; it’s nearly myopic idealism–and perhaps not so optimistic after all? Fuchs identifies himself as an American pragmatist, but his pragmatists of choice are later William James and Richard Rorty, not Charles Sanders Peirce–in other words, pragmatism at its mushiest.

David Mermin, who is more cautious than Fuchs or Hardy, makes this cryptic statement:

MERMIN: In my two papers, I used the phrase “has physical reality” to mean “can be accounted for in a physical theory,” particularly when I insisted that conscious experience has reality, but not physical reality….

“Physical reality” is not, as I seem to have implicitly maintained fifteen years ago, just a subset of “reality.” Neither is contained in the other. Conscious awareness belongs to reality and not to physical reality, but correlation belongs to physical reality and not to reality.

Is this a variant of Donald Davidson’s anomalous monism, where consciousness lacks clear correlative properties?

And there are some cautious sorts like Wojciech Zurek and Anthony Leggett who both say that the story is simply too incoherent to take sides, even though their research approaches drastically differ. The endearing New Yorker Daniel Greenberger (he’s been at City College since 1963!) goes even further and says we most likely don’t know much of anything about anything. They lack the intuition and/or the desire to take one or more unpalatable metaphysical bullets over others:

Nonlocality (“spooky action at a distance”)

Tychic indeterminism/probabilism

Advanced action (backwards causation)

Arbitrary fine-tuned kludges (in de Broglie-Bohm and maybe GRW)

Multiple worlds of one form or another

Observer-dependence

Anti-realism

I couldn’t precisely map which of these apply to which interpretations, but they are the intuitive concepts that one or more of the interviewees repeatedly appeal to as problematic, repellent, unacceptable, or incoherent. But not one is rejected by everyone and each is embraced by at least one. (I think only Leggett goes for advanced action, which Huw Price also has shown an interest in elsewhere.)

As far as I can tell, and here I am going out on a limb as far as the limits of my understanding, the information-theoretical approach is the most effective giant-killer, sweeping away a fair number of the above points while embracing and exacerbating the final two.

Well, information is a funny thing. I worked with it formally for years and still do, and it’s remarkable how much you can do with it without even being able to define what information is. Well, no, but the definition is pretty darn prosaic: information is bits arranged in sequences which can be analyzed and manipulated mathematically. The immediate question everyone has: “information to whom?” No one in particular. Or, rather, anyone who’s willing to call it information. And so the relation of “information” to “reality” is still pretty fuzzy, or at least as fuzzy as the relation of mathematics in general to reality. Is it just a new and improved modeling tool?

Wojciech Zurek, who has worked on the information-theoretic side but hesitates to make any metaphysical pronouncements, still makes a methodological prediction:

ZUREK: This separation of information from states was tenable in classical physics, but it breaks down in quantum theory—it breaks down in our universe. I think that by now many people recognize how central information is to quantum physics. On a technical level, this started with Heisenberg and his indeterminacy principle. But even with all that we know now about the interplay of quantum physics and information (including Bell’s theorem, the no-cloning theorem, quantum error correction, and so on), I sense that the real mystery is still barely touched.

But conventional Platonism doesn’t deal well with information as a fundamental ontological category, since information would have to instantiate Formal Reality, not constitute it. So my feeling is that as long as information is seen to be fundamental, the Platonists are going to lose and the subjective idealists will win–from an intuitive standpoint if nothing else.